Patients with high blood pressure (hypertension) can be divided into two groups, based on their responses to diets low in sodium. The two groups have been designated modulators and non-modulators. Modulators increase the production of a hormone called aldosterone when administered a diuretic drug called furosemide. Non-modulators do not. Similarly, modulators increase the synthesis of aldosterone when another hormone called angiotensin-2 is given (while on a low-salt diet), whereas new modulators do not. This study is designed to determine if non-modulation is an heritable defect that might be present even before hypertension is detected. An attempt is also being made to correlate the presence of non-modulation with movement of ions across red cell membranes. The approach is to determine modulation status within sibling pairs (both those with hypertension and normal pairs) to assess familial aggregation, and then to do segregation analysis in pedigrees in an attempt to isolate genes responsible for hypertension.